Adjustable tubular condenser



July 10, 1956 c 2,754,458

ADJUSTABLE TUBULAR CONDENSER Filed Feb. 2, 1954 INVENTOR.

TORNEY United States Patent ADJUSTABLE TUBULAR CONDENSER Charles L. Shull, Horseheads, N. Y.

Application February 2, 1954, Serial No. 407,759

3 Claims. (Cl. 317-249) The present invention relates to an adjustable tubular condenser and more particularly to a trimmer condenser for high frequency oscillating electrical circuits.

The present disclosure is an improvement on the trimmer condenser disclosed in applicants prior application Serial No. 263,540, filed December 27, 1951, now Patent No. 2,708,729.

It is an object of the present invention to provide a novel trimmer condenser which is simple and rugged in construction and of short over-all length relative to condensers of similar capacity.

It is another object to provide such a device which is free from projecting operating devices which might be subject to accidental deformation.

It is another object to provide such a device in which, during adjustment of the condenser, the inner electrode is traversed directly and is prevented from rotation by a plurality of elastic clamping members.

It is another object to provide such a device in which the clamping members also serve to complete a direct electrical connection to the inner electrode.

It is another object to provide such a device in which the traversing means for the inner electrode comprises a pair of concentric threaded connections of opposite hand, the adjustment being effectuated by rotation of an intermediate double threaded sleeve.

It is another object to provide such a device in which said traversing means comprises self-contained stops for limiting the travel of the inner electrode in both directions.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawing, in which:

Fig. l is a longitudinal substantially mid-sectional view of a preferred embodiment of the invention shown on an enlarged scale, the inner electrode and its screw shaft being shown in elevation; and

Fig. 2 is a section on a further enlarged scale taken substantially on the line 22 of Fig. 1.

In Fig. 1 of the drawing there is illustrated a tube 1 of suitable dielectric material having an outer electrode 2 in the form of a metallic sleeve mounted on one end and extending somewhat less than half the length of the tube. The opposite end of the tube 1 is mounted in any suitable manner as indicated at 3 on a metallic bushing 4. Said bushing has a fiange 5 forming an abutment for the end of the tube, and a cylindrical extension 6 which is exteriorly threaded as indicated at 7 for the reception of a nut 8 for clamping the bushing in a panel 9.

A cylindrical inner electrode 11 is slidably mounted within the dielectric tube 1, and a shaft 12 having a square cross-section is rigidly fastened at one end within the inner electrode in any suitable manner as by means of a press fit and/or a soldered junction as indicated at 13. The shaft 12 is threaded for the major portion of its length as indicated at 14, the threads being formed on the corners of the shaft, leaving the fiat surfaces 15 be tween the threaded corners as shown more particularly in Fig. 2.

2,754,458 Patented July 10, 1956 The bushing 4 is provided with four projecting arms 16 terminating in flat surfaces 17 which bear on the flats 15 of the screw shaft. The arms 16 are slightly elastic and are biased to spring inwardly so that when the screw shaft is introduced between them they clamp the shaft firmly, preventing it from rotation and forming an intimate electrical connection to the shaft and consequently to the inner electrode 11.

The bushing 4 is internally threaded as shown at 18 for the reception of a traversing sleeve 19 which is also both internally and externally threaded as shown at 21 and 22 respectively, the inner threads receiving and cooperating with the threads 14 of the screw shaft 12.

The inner threads 21 of sleeve 19 and the threads 14 of screw shaft 12 are of the opposite hand from the external threads 22 of the sleeve and the internal threads 18 of bushing 4. Consequently, traversal of the sleeve 19 by rotation within the bushing 4 causes the screw shaft 12 to be traversed relative to the sleeve 19 in the same direction. It follows that when the sleeve 19 is rotated, the screw shaft 12 and inner electrode 11 are traversed substantially twice as far as said sleeve. Rotation of sleeve 19 to adjust the inner electrode and thereby vary the capacity of the trimmer may be eflectuated in any suitable manner as by means of a screw driver slot 23.

Spring means are provided to assist in securing and maintaining accurate adjustment of the inner electrode 11 and to prevent lateral movement of the electrode in the dielectric tube due to shocks or rough handling. This means comprises an annular dished spring member 24 riveted on the free end of the inner electrode as shown at 26, and having a plurality of elastic fingers 25 pressing out against the interior of the tube.

In the utilization of the condenser as a circuit unit, electrical connections are made to the outer electrode 2 as by means of a connector element 27, and to the bushing 4. The capacity of the condenser is then adjusted by rotation of the sleeve 19, the consequent longitudinal movement of which is multiplied and transmitted to the screw shaft 12 and inner electrode 11. During this operation, the ends 17 of the clamping arms 16 press firmly on the flat sides 15 of the screw shaft 12 and hold the screw shaft firmly against lost motion while maintaining perfect electrical contact therewith. The limits of travel of the inner electrode are defined in the one direction by the abutment of the end of sleeve 19 against the inwardly projecting ends of the clamping arms 16 of bushing 4 as shown in Fig. 1. Travel in the opposite direction is limited by the engagement of the inner electrode with the ends of said arms. There is thus no danger of inadvertently fracturing the dielectric tube by over-travel of the inner electrode. This arrangement provides a maximum range of adjustment for the short over-all length of the device, and avoids any slender unsupported pins or shafts which might be subjected to twisting or bending.

Although but one form of invention has been shown and described in detail, it will be understood that changes may be made in the precise form and arrangement of the parts without departing from the spirit of the invention.

I claim:

1. In a trimmer condenser a ceramic dielectric tube, mounting means therefor including a metallic bushing rigidly attached to one end thereof, an outer electrode in the form of a metallic sleeve sheathing the tube for a portion of its length, a cylindrical inner electrode slidably mounted in the tube, and means for traversing the inner electrode comprising a sleeve threaded in said bushing and a metallic screw shaft fixed at one end to the inner electrode and oppositely threaded in the sleeve, said screw shaft having a plurality of oppositely located longitudinally extending flat surfaces; and means for preventing imman nt the screw shaft and forming a direct electrical connection from "the screw shaft to said bush-ing inc-hid" ing a plurality of elastic metallic arms extending into the tube from the bushing and terminating in fiat surtaces bearing fr'ictionally on the fiat surfaces of the-screw shaft; the arms -of the bushing being formed to embrace the inner end of -the threaded sleeve and to provide an abutment limiting the inward travel of the sleeve and consequ'e'ntly prevent the inner electrode from contacting the end of the ceramic tube.

2. A -trimmer condenser as set forth in claim 1 including further spring stabilizing means fi'xedon the free end of the inner electrode bearing frictionally on the inner surface of the dielectric tube.

3. A trimmer condenser as set forth in Claim '1. in which 2,109,880 DoW Mar. 1, 1938 2,338,271 Ulanet Jan. 4, 1944 2,578,608 Shull Dec. 11, 1951 2,607,326 Barnes Aug. 19, 1952 2,654,034 Morton Sept. 29, 1953 FOREIGN PATENTS 263,948 Great Britain J an. 10, 1927 540,279 Great Britain Oct. 10, 1941 600,033 Great Britain Mar. 30, 1948 

